JP2013503052A - Method and apparatus for the production of spray coatings made of reactive plastics - Google Patents

Abstract

  The present invention relates to a method for producing layers and molded parts of reactive plastic material in which reactive components are mixed in a spray channel with a mixed gas on a plurality of sides. Furthermore, the invention relates to a device enabling a corresponding method.

Description

  The present invention relates to a method for producing a layer of reactive plastic material and a molded part in which reactive components are mixed with one another in a spray channel in several respects by a mixed gas. Furthermore, the invention relates to an apparatus enabling such a method.

  The use of different reactive plastic materials for producing molded parts is well known from the prior art. When the reactive plastic material is applied to a substrate, spraying is usually the optimal application technique. Polyurethane is often used as the plastic material, but the techniques described are applicable to other reactive plastic materials.

  Various applications of the above spray technique are described in Kunststoffhandbuch, Vol. 7, Polyethane, Carl Hanser Verlag.

  In polyurethane processing, the mixing of the liquid reaction components takes place in the mixing head and a distinction can be made between high pressure mixing and low pressure mixing. In both cases, spray application is achieved by a downstream sprayer system.

  In the low pressure mixing method, the mixing energy required to mix the reaction components is introduced by a dynamic stirrer or a static mixing device. The volume of the mixing chamber is relatively large compared to the mixing head used for high pressure mixing and must be cleaned with a suitable cleaning agent or compressed air after the mixing process is complete. In particular, when processing highly reactive polyurethane systems, the low pressure mixing head has a design related tendency to accumulate mixing chamber deposits and therefore prone to clogging after prolonged operation.

  In the high pressure mixing method, the pressure energy of the reaction component is changed to kinetic energy by the nozzle. By injecting the components from the nozzle into a relatively small mixing chamber, the kinetic energy is concentrated in the space and used to mix. The mixing chamber is cleaned with a mechanical suction tool, allowing a short interruption of the spraying process. This advantage is a feature of the high pressure mixing head that is important for the formation of a constant layer thickness in the robot guided spray process. This is because the moving speed decreases just before the branch point of the robot path, and thus changes the ratio of surface area to material output. The possibility of a short interruption of spray application makes it possible to shift the branch point to a region outside the area to be sprayed.

  A nebulizer system downstream of the mixing process serves to divide the reaction mixture into individual droplets. A single nozzle (airless high pressure spray) and a double nozzle (pressure spray) with external and internal mixing are used for spraying. The advantage of a double nozzle with internal mixing is that the double nozzle has a relatively large cross-sectional area of flow and can also spray liquids containing coarse particles. Another advantage is that changes in viscosity or volume flow have little effect on the shape of the spray jet. This property is quite important for the processability of the polyurethane system rich in solids according to the following method, but the possibility of variably adjusting the solid fraction brings a large change in the viscosity.

  Different spray systems are also described in the prior art. For example, air and / or gas injection openings in the corresponding flow channels are known from US-A-3932253, DE 102007016785A1 or US-A-6131823.

  A device for directing the reactants from the two supply conduits to the mixing tube as required is known from DE 2700488A1. The mixing tube has a number of nozzles B1, D1, B2 and D2, and the high pressure medium introduces not only the gas, for example, but also the components of the main liquid stream into the tube and mixes it with the main liquid stream. The nozzles are installed opposite to each other, and turbulent flow is generated in the mixing tube.

  However, it is necessary for many applications to mix additional components with the reactive plastic material. On the other hand, these can be fibers that allow higher stability of the product. Other possible additives include flame retardants, antioxidants, UV protection agents and the like. The mixing of the solid, liquid and / or gaseous components with the reaction mixture is described in the prior art by different methods. In WO 03/037528 A2, the polyol and isocyanate components are mixed together with a filler in a mixing head. This allows the polyurethane components to be mixed with the filler as well as with each other. However, it is disadvantageous in that the mixing head can be damaged by the filler. The filler itself can also be damaged by shear forces that can occur in the mixing head.

  Alternatively, the additive can be added to the reaction mixture after mixing. This is often done by mixing a spray jet of reactive plastic material with a spray jet of the corresponding filler. This is known, for example, from DE 2517864 A1, US Pat. No. 3,302,891, WO 2009/052990 A1 or EP 1458494 B1. In the method described there, the mixing head is not damaged by the filler. Also, the filler itself is not damaged. However, the wetting of the filler and reaction mixture is often insufficient.

  The still unpublished patent application PCT / EP2009 / 001007 describes a newly developed method for introducing solids into a polyurethane spray jet sprayed with pressurized gas. The introduction of solid particles takes place by means of a spray gas as particle carrier into the liquid reaction mixture still contained in the spray accessory (reaction jet) (reaction jet). An apparatus capable of the above method is described, for example, in the unpublished PCT application PCT / EP2009 / 003545. From an accessory with an integrated mixing surface downstream of the mixing head, the gas / solid mixture is fed tangentially to the liquid reaction mixture and mixed by the resulting rotational twist, only afterwards as a spray jet as a multiphase mixture Released from the nebulizer.

  Prior to the development of this method, the spraying and mixing of solids with a dual nozzle gas stream supply with internal mixing was not provided in the polyurethane spraying process. The spray device only has the function of a pressure sprayer, and a short residence time of the reaction mixture in the spray device as well as a barrier-free channel shape without dead space is preferred to maintain cleanliness.

  However, in experiments carried out with the spray apparatus described there by the method described in PCT / EP2009 / 001007, it was found that the wetting of the particles may be insufficient when processing higher solids. .

  High solids at a small particle size provide a large surface area to the reaction mixture but cannot be well mixed and wetted with the reaction mixture due to the short residence time in the mixing zone. Furthermore, solid particles at high density accumulate by centrifugal force in the wall region of the flow channel and can only be mixed with the reaction mixture conditionally for densification. For example, for a mixture output of 100 g / sec and a solid content of 70% by weight (barium sulfate), this effect is seen as an annular structure of unwet solid particles as the mixture is released.

  Another indication of inadequate mixing, for example local accumulation of solids due to centrifugal forces, is swirl erosion in the flow channel. If the flow is turbulent and the solid particles are distributed homogeneously, a certain surface wear is seen when using uncured spray accessories.

US Patent Application No. 3,923,253 German Patent Application No. 102007016785A1 US Pat. No. 6,131,823 German Patent Application Publication No. 2700488A1 International Publication No. 03 / 037528A2 Pamphlet German Patent Application Publication No. 2517864A1 US Patent Application Publication No. 3302891 International Publication No. 2009 / 052990A1 Pamphlet EP 1458494B1 specification PCT / EP2009 / 001007 PCT / EP2009 / 003545

Kunststoffhandbuch, Volume 7, Polyethane, Carl Hanser Verlag

  The object of the invention is therefore to produce reactive plastic materials, in particular polyurethane layers and molded parts, in particular by spray application, which can process higher solids and at the same time ensure a homogeneous wetting of these solids. It is to develop a method and apparatus for doing this.

  As known from DE 102005058292A1, a light and small design is advantageous for the spraying process using robots. The robot-guided mixing head contains very fast changes in movement, and the advantages of metering and small design for the manually-guided mixing head are self-evident. Accordingly, a further object of the present invention is to provide a device having a small and lightweight design. When such an apparatus is used, a high solid content can be introduced into the reaction mixture. Furthermore, the device is wear resistant, has a spraying capability and is easy to clean. In particular, the device according to the invention allows for short application intervals and is also compatible with commercially available casting / mixing heads.

  The object of the invention could be achieved by a method in which the mixing zone was extended and several mixing surfaces were introduced therein.

FIG. 1a shows a cross-sectional view of a device according to the invention. FIG. 1b shows the mixing principle in the device according to the invention. FIG. 2a shows a modular mixer according to the invention without an upstream PUR mixing head, in which the mixing surfaces can be combined as required according to the required mixing performance, for example by mixing parts in the form of disks. Show the design. FIG. 2b shows the corresponding mixing principle. FIG. 3a shows a cross-sectional view of the device according to the invention. FIG. 3b shows the relevant mixing principle.

  In the first embodiment, the reaction mixture, in particular the polyurethane reaction mixture, was passed from the mixing head to the device according to the invention. The solid / gas mixture was added from the inlet. Each mixing surface is composed of at least one gas channel through which a gas flow leads to the spray channel. According to the invention, the direction of the gas flow is directed out of the center of the spray channel when entering the spray channel. The tangential arrangement gives a radial flow component to the axial flow. Due to the radial flow component, the components, in this case the reaction mixture and the solid, are vigorously mixed together. The gas channels and injection openings are arranged to provide opposing twist directions on the mixture beyond the flow path at each mixing surface. The twist direction of one surface faces the twist direction of the next mixing surface. The first mixing surface, ie the first at least one gas channel, is above the injection opening for the solid-gas mixture.

  FIG. 1a shows a cross-sectional view of a device according to the invention. For simplified practical expression, the miscible gas channel leading to the mixing space is not drawn tangentially in this figure and in the following cross-sectional views.

  FIG. 1b shows the mixing principle in the device according to the invention. In the nozzle according to the invention, the radial flow component is provided by a miscible gas in the spray channel in which the reaction mixture flows axially. This again causes turbulence of the reaction mixture. On the next mixing surface, the solid-gas mixture is introduced through a suitable inlet. The inlet is also arranged tangentially for further mixing here. The twist direction caused by the solid-gas mixture faces the twist direction caused by the mixed gas at the first mixing surface. In the further mixing plane, the mixed gas is injected again from the appropriate gas channel.

  Here, the tangential injection again causes an axial radial turbulence of the reaction mixture. The twist direction of the reaction mixture produced here again faces the twist direction caused by the introduced solid / gas mixture. Good performance of mixing between the solid and the reaction mixture is ensured by the opposing twist direction. Also, the reaction mixture itself is thoroughly mixed. For this purpose, it is important that a gas inlet for the mixed gas is provided upstream of the inlet for the solid / gas mixture. Thus, the device according to the invention has at least one gas inlet on each of at least two surfaces, ie one upstream of the inlet for eg a solid / gas mixture and one downstream of these inlets. Have.

  According to the invention, it is not only possible to introduce a solid-gas mixture into the reactive stream from the inlet. It is also possible to introduce individual components of the reaction mixture from the inlet. It is further possible to add solid, liquid and / or gaseous additives to the reaction mixture. However, it is always conceivable that there is a mixing surface upstream of these injection openings, i.e. injecting a mixed gas into the flow channel.

  Preferably, the device according to the invention has a further mixing surface. As shown in FIG. 1b, each at least one gas inlet is such that at said further mixing surface, the twisting direction initiated by the mixing gas is different from the twisting direction of the mixing surface immediately above, ie facing each other. Placed in. In particular, the device according to the invention has a mixing surface with at least one gas inlet of more than 2, in particular more than 4, in particular more than 6.

  Thus, the gas flow vector acts as a static mixer or stirrer. According to the invention, each mixing surface has at least one, in particular two gas inlets.

  Surprisingly, experiments with the apparatus according to the invention have been shown to be qualitatively good so that the opposing torsional direction and significantly higher shear forces in the direction of the mixing channel can avoid mixing the reaction components by the upstream PUR mixing head. It was shown to produce some mixing effect.

  FIG. 2a shows a modular mixer according to the invention without an upstream PUR mixing head, in which the mixing surfaces can be combined as required according to the required mixing performance, for example by mixing parts in the form of disks. Show the design. The initial inlet diameter is used here to introduce the reactive components A and B of the reactive plastic material. FIG. 2b shows the corresponding mixing principle. Two injection openings are shown here. However, additional injection openings can be provided in the same plane according to the invention.

  Therefore, in the method according to the invention, at least two components are introduced from the outside through the two inlets into the spray channel in the nozzle, respectively. The spray channel has at least two mixing surfaces for injecting at least one miscible gas from at least one tangentially arranged gas channel, and at least one of these mixing surfaces is used for component injection. Provide upstream of the inlet and other mixing surfaces downstream thereof. “Upstream” and “downstream” are understood according to the direction of flow of the reactive stream.

  Thus, the mixing head function works exclusively with the device according to the invention, the mixing / spray nozzle, so that a very small and light weight design without moving parts and seals can be achieved at low cost. Furthermore, the high-pressure metering system with high costs can be omitted by the present invention.

  In the device according to the invention, the spray channel is inside the mixing nozzle. The atomizing channel is separated from the surrounding gas space by a wall, and the mixed gas can be injected from at least one gas channel into the atomizing channel and from the gas space into the atomizing channel at at least two mixing surfaces, respectively. Therefore, only one gas connection for the nozzle according to the invention is required. The mixed gas flows from all existing gas channels into the spray channel at the same pressure. In one plane, there is at least one gas channel that passes from the gas space to the spray channel. However, preferably more than one gas channel is on one side and preferably two gas channels facing each other are on one side.

  In a preferred embodiment, the cylindrical mixing zone has a tapered nozzle outlet. Such a design is a very simple design of the spray mixing nozzle according to the invention.

  The principle of pressure mixing causes a subsequent density reduction of the polyurethane matrix and results in gas loading of the mixture which is undesirable for certain applications. For example, in a functional layer for sound reduction according to the spring mass principle, a density of> 2 mass layers is clearly required. In such cases, the gas loading caused by the mixing process simultaneously with the addition of solids has the opposite effect.

  Accordingly, in a further embodiment, the object of the present invention is to provide a gas in which a hollow cylinder is applied to the interior of the spray channel and in which the mixed gas stream is injected tangentially from the gas channel into the spray channel. This is achieved by a spray mixing nozzle provided with a distributor. FIG. 3a shows a cross-sectional view of the device according to the invention. FIG. 3b shows the relevant mixing principle. The mixed gas injection flows are injected tangentially and face each other. In the outer spray channel, the corresponding reactive components as well as solid, liquid and / or gas additives can also be introduced from the outside. The inlets for the reactive component and additive are provided on two different sides, introducing the reactive component on one side and introducing the additive on different sides. Between these surfaces is at least one mixing surface for injecting a mixed gas.

  Such a mixing space shape ensures mixing between the individual reactive components and additives, in particular solids. The flow from the gas from the inside to the outside allows for sufficient mixing even when the amount of pressurized gas is reduced, thus reducing gas loading. Mixing is enabled by the opposing, tangentially injected miscible gases, and thus by the opposing twist directions at the individual mixing surfaces. The introduction of reaction components and additives is also performed so that the twist direction changes in the nozzle.

  The shape of the mixing space composed of a hollow cylinder has a gas distributor at the center thereof. Due to the formation of the annular flow with small gaps, the mixing action of the pressurized gas flow can be prevented from being lost in the middle of the mixing space (in the middle of the space of the flow channel) relative to the cylindrical mixing space. Furthermore, the mixing effect of the gas flow is not adversely affected by the centrifugal force.

  In the arrangement described in FIG. 3a, maintaining the cleanliness of the pressurized gas channel is such that the mixing chamber wall boundary to the outside is completely closed after supplying the solids, so that the wet solid particles are fed into the gas channel by centrifugal force. This is advantageous because intrusion can be eliminated. In the corresponding gas flow, it is not possible for the mixture to enter the mixing gas channel by backflow.

  In a corresponding design, the position of the central gas distributor can be shifted axially, so that the volume in the mixing space immediately before the discharge opening and thus the flow rate can be adjusted. This action can be used, inter alia, to affect the spray image.

  If necessary, the spray mixing nozzle described in FIG. 3a can be combined with a conventionally used PUR mixing plant, so that the existing mechanical technology can be used continuously.

  Cleaning of the spray mixing nozzle according to the invention can be carried out with pressurized gas according to the prior art. The cleaning method begins by maintaining or increasing component flow switching and pressurized gas supply. This procedure also allows short-term shot interruptions due to similarities in high-pressure technology, which is advantageous in robot-guided spray application, for example, for forming a uniform thickness of the spray layer, as described above.

  In a specific embodiment, the gas channel intrusion angle is obliquely below the component surface and in the direction of contact and component flow. However, this gas flow penetration shape is only possible by using an increased gas flow rate or a faster flow rate because the slope in the direction of the mixture flow helps the mixture to penetrate the gas channel.

  Besides the number of mixing surfaces, the gas flow rate, the direction of rotation of the gas flow and the angle of penetration of the gas flow, influences on the mixing process can also be given by pulsing the gas flow. In pulsating gas supply, it is advantageous when each mixing surface is supplied with a high frequency pulse of pressurized gas. The pressurized gas supply of the device from FIGS. 1a and 2a is present on the outside and provides ideal conditions for this variant.

  A solid-gas mixture can not only be introduced into the reaction mixture by means of the device according to the invention. It is also possible to introduce the reaction components into the nozzle as a pre-sprayed aerosol using a pressurized gas stream. Mass differences in the mixing ratio of the reaction partners can be corrected by adapting to the volume flow and particle size. For example, mixing ratios from 100 to 1 cannot normally be mixed with a high-pressure mixer, but can be successfully mixed or processed up to a coating speed of 50 g / sec.

  In other embodiments, it is further possible to inject hot gas into the reaction mixture from an existing inlet. This allows for thermal activity of the reactants. Due to the short mixture residence time, gas temperatures up to 600 ° C. are used in the process according to the invention.

  It is normal practice to influence the process of reaction of the reactive plastic material from the heated mold surface or temperature control mixture components. The hot air spraying process allows the same effect, but can be changed during removal of the mixture if necessary. Thus, for example, large area components can be adapted to the process of reaction of the mixture over the entire duration of spraying, thereby enhancing the productivity of the process. Furthermore, the distribution of the reaction mixture on the oblique plane can also be influenced reliably.

  According to the invention, the reactive plastic material is preferably polyurethane. The reactive components used are therefore in particular the polyol and isocyanate components. Components known from the prior art can be used.

  According to the invention, the fibers are preferably introduced into the reaction mixture from the inlet. Other solids that may be added include, for example, flame retardants, stabilizers or antioxidants. Also, the same function can be supplied by a liquid aid that can be supplied.

Claims (17)

  A method for producing a layer of reactive plastic material and a molded part, wherein at least two components are respectively introduced from the outside into a spray channel of a nozzle for mixing them, said spray channel comprising at least one mixing Having at least two mixing surfaces into which the sex gas is injected from at least one tangentially arranged gas channel, and providing at least one of the mixing surfaces upstream of the inlet for said component A method characterized by.   The method according to claim 1, characterized in that the mixed gas is injected into the spray channel such that the direction of the gas stream flow is out of the center of the spray channel when entering the spray channel.   3. A process according to claim 1 or 2, characterized in that the polyol and isocyanate components are introduced into the nozzle.   A nozzle is connected to the mixing head in which the reaction mixture, in particular the polyurethane reaction mixture flows axially into the spray channel, and further components are mixed with the reactive stream from the inlet. The method in any one of -3.   5. A method according to claim 4, characterized in that solid, liquid and / or gaseous components are added to the reactive stream from the inlet.   The gas channel is arranged to provide a radial flow component on the axial flow of the reaction mixture by injecting a mixed gas into the surface, the radial flow component being in one direction at one of the surfaces and the next 6. A method according to any one of claims 1 to 5, characterized in that the surfaces have opposite directions and that the introduction of components from the inlet is also regarded as a surface.   A mixed gas is injected tangentially into the nozzle from at least one gas channel in each of at least three planes from a hollow cylinder provided inside the nozzle, said nozzle being further inlets for various components 2. The method according to claim 1, characterized in that it has at least two different faces.   The gas channel is arranged to provide a radial flow component on the axial flow of the reaction mixture by injecting a mixed gas into the surface, the direction of the radial flow component on one surface being the radial flow component on the next surface The method according to claim 7, characterized in that the inlet for the component is also considered to be a surface.   Said nozzle has on its inside a spray channel separated by a wall from the surrounding gas space, and the mixed gas is transferred from at least one gas channel to the spray channel and from the gas space to the spray channel, respectively, on at least two mixing surfaces. An apparatus for producing a layer of reactive plastic material and a molded part by the method according to claim 1, characterized in that it is injected.   The gas channel is arranged such that the flow direction of the gas flow is out of the center of the spray channel when entering the spray channel, and this tangential arrangement provides a radial flow component to the axial flow in the spray channel The device according to claim 9, wherein:   The gas channel and the inlet are arranged such that opposing twist directions are provided on the mixture over the flow in the spray channel, the twist direction facing the twist direction of the next face on one side, Item 9. The apparatus according to Item 9 or 10.   The spray channel is connected to the mixing head, and solid, liquid, reactive gas and / or mixed gas is introduced from the inlet into the reactive flow flowing axially from the mixing head, for the mixed gas. 12. Device according to any of claims 9 to 11, characterized in that at least one gas channel is provided upstream of the inlet.   Device according to any one of claims 9 to 12, characterized in that the two gas channels face each other in one plane.   The inside of the spray channel has a hollow cylinder, and a gas distributor for injecting a mixed gas flow in a tangential direction from the gas channel connected to the spray channel is provided at the center thereof. An apparatus for producing a layer of reactive plastic material and a molded part by the described method.   The inlet leads from the outside to the spray channel on at least two different sides, characterized in that the reactive component and at least one solid, liquid and / or gas additive can be mixed from the inlet. The apparatus according to claim 14.   The gas channel is arranged to impart a twist to the reactive component flowing in the axial direction, and the twist direction in one plane lasting for the surface mixing the reactive component and the at least one additive is the next plane 16. A method according to claim 14 or 15, characterized in that it differs from the twist direction of the.   17. A device according to any one of claims 14 to 16, characterized in that the two gas channels face each other in one plane.

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